1. Field of the Invention
The present invention relates generally to a method of providing burst timing in a base station (BS) of a mobile communication system, and in particular, to a method of providing forward and reverse burst timing with respect to the time of using a supplemental channel (SCH) and a supplemental code channel (SCCH) for rapid transmission of a large amount of data in a BS, taking into account a discontinuous transmission (DTX) mode.
Specifically, the present invention relates to a method of providing burst timing definable with respect to the use time of a physical channel and the start and end time of data and a method of supporting an AAL5 protocol for high-speed data transmission between BTSs by a base station transceiver system (BTS) and a base station controller (BSC) in a mobile communication system under a ratio channel environment which allows high-speed data processing.
2. Description of the Related Art
Typical CDMA (Code Division Multiple Access) mobile communication systems provide mainly voice service, but the IMT-2000 (International Mobile Telecommunications-2000) standard has been developed to additionally provide high-speed data transmission. IMT-2000 mobile communication systems are capable of transmitting high quality voice and moving pictures, as well as Internet browsing.
A CDMA mobile communication system is comprised of a BS including a BTS and a BSC, a mobile switching center (MSC), and a mobile station (MS). Radio links between an MS and a BTS include a forward link directed from the BTS to the MS and a reverse link directed from the MS to the BTS.
All channels are divided into physical channels and logical channels. A logical channel .is set on a physical channel and it is possible that a plurality of logical channels are set on one physical channel. If the physical channel is released, the logical channels are automatically released. However, a physical channel is not necessarily created to set up a new logical channel. If a physical channel that can carry another logical channel has already been occupied for other logical channels, all that should be done is to assign the new logical channel to the already established physical channel.
Physical channels are categorized into dedicated channels and common channels according to their characteristics. The dedicated channels are so named because they are dedicated to communication between a BS and a particular MS, and include a fundamental channel (FCH), a dedicated control channel (DCCH), and a SCH. The FCH, compatibly used with TIA/EIA-95-B, transmits voice, data, and signaling signals. The common channels indicate channels, commonly shared by a BS and a plurality of MSs. A forward physical channel transmitted to the MSs from the BS is a paging channel, and a reverse channel transmitted to the BS from an MS is an access channel. These common channels are compatible with IS-95-B.
Data communication in a mobile communication system is characterized by bursts of concentrated data transmission interspersed between long periods of no data transmission. Accordingly, the next generation mobile communication system is developed in such a way that it can operate in a discontinuous transmission (DTX) mode in which a dedicated channel is only assigned when there is data to be transmitted.
In the DTX mode, frame data is transmitted only when transmission data exists in a wired communication system or in a mobile communication system. Hence, if transmission data is absent for a predetermined time period in the DTX mode, frame data is not transmitted. The DTX mode has the distinctive advantages of minimum transmission power, reduction of the strength of interference which adversely affects the system, and increase of total system capacity.
The DTX mode is supported on a DCCH and an SCH. Because of this, the DCCH can be used as a control channel which provides an efficient packet service. In DTX mode, null frames are transmitted on the DCCH for power control and no data is transmitted on the SCH. Considering limited radio resources, BS capacity, and power consumption of an MS, dedicated traffic and control channels are connected only during actual data transmission and released during non-transmission periods while in the DTX mode. Communication is conducted on a common channel while the dedicated channels are released. As a result, the usage efficiency of the radio resources is increased. Various channel states are set according to channel assignment and the presence or absence of state information in order to implement the DTX mode.
FIG. 1 is a state transition diagram for a typical packet service in a mobile communication system.
Referring to FIG. 1, a packet service is comprised of an active state 11, a control hold state 12, a suspended state 13, a dormant state 14, a packet null state 15, and an initialization state 10. Service options are connected in the control hold state 12, the active state 11, and the suspended state 13. It is to be noted herein that the present invention pertains to a base station which supports the DTX mode on an SCH and a DCCH in the active state 11 and the control hold state 12.
FIG. 2 illustrates a reference model of 3G IOS (Interoperability Specifications) for a digital air interface between an MSC and a BS and between BSs in a general mobile communication system.
Referring to FIG. 2, an A1 interface and an A2/A5 (exclusive for circuit data) interface are defined for transmitting a signal and transmitting user information, respectively, between an MSC 20 and a BSC 32. An A3 interface is defined to connect a target BS 40 to a frame selection/distribution function unit (SDU) 34 of a source BS 30 for soft/softer handoff between BSs. Using the A3 interface, signaling and user data are transmitted between the target BS 40 and the SDU 34 of the source BS 30. An A7 interface is defined to transmit/receive signals between the target BS 40 and the source BS 30 for soft/softer handoff between BSs. Wired communications links between the BSs 30 and 40 and between the BS 30 and the MSC 20 are a forward link directed from the MSC 20 to the BS 30, a reverse link directed from the BS 30 to the MSC 20, and a link connected between the BSs 30 and 40. The MSC 20 has a call control & mobility management block 22 and a switch 24. The MSC 20 is connected to a data network (not shown) such as the Internet via an inter-working function (IWF) block 50.
FIG. 3 illustrates a signal flow by which an SCH is established between a source BS and a target BS in conventional technology. This procedure is executed to establish an SCH between the source BS and the target BS when a large amount of high rate data is received from an external Packet Data Service Node (PDSN) or data is to be transmitted by assigning the SCH upon call origination from an MS.
Referring to FIG. 3, the source BS 30 recognizes that an MS has origination/termination data to transmit/receive to/from another MS or the PSDN (3a). Then, the source BS 30 determines a traffic burst required during service instance support, selects the target BS 40 which will assist the determined traffic burst, and transmits a burst request message (A7-Burst Request msg.) to the target BS 40, requesting reservation of necessary resources (3b). The target BS 40 checks whether part or all of the requested resources are available and transmits a burst response message (A7-Burst Response msg.) inlcuding information about the resources committed for the traffic burst to the source BS 30 (3c). Meanwhile, the source BS 30 awaits receipt of the burst response message for a first predetermined time. Tbstreq after transmission of the burst request message. Upon receipt of the burst response message within Tbstreq, the source BS 30 prepares a set of frame selectors based on the information of the burst response message and transmits a burst activate message (A7-Burst Activate msg.), which indicates a set of the committed resources to be actually used, to the target BS 40 (3d). If timer Tbstreq expires, the source BS may choose to send an A7-Burst Request message again.
Meanwhile, the target BS 40 awaits receipt of the burst activate message for a second predetermined time Thstcom after transmission of the burst response message. If the target BS 40 receives the burst activate message within Tbstcom, it transmits a connect message (A3-connect msg.), which is for connecting all cell resources to be used for the traffic burst to the designated frame selectors, to the source BS 30 (3e). The source BS 30 transmits a connect acknowledgment message (A3-connect Ack msg.) to the target BS 40, notifying the target BS 40 that physical channels to support the traffic burst are ready (3f). If timer Thstcom expires, the target BS may decommit all radio resources committed for the cell(s) included in this message. Meanwhile, the target BS 40 awaits receipt of the connect acknowledgment message for a third predetermined time Tconn3 after transmission of the connect message. If the target BS 40 receives the connect acknowledgment message within Tconn3, it transmits a burst activate acknowledgment message (A7-Burst Activate Ack. msg.) to the source BS 30 (3g). If timer Tconn3 expires, the BS shall include all new cells that would have been added by the A3-Connect message to the list of non-committed cells in the A7-Burst Response message.
Meanwhile, the source BS 30 awaits receipt of the burst activate acknowledgment message for a fourth predetermined time Tbstact after transmission of the burst activate message in step 3d. If the source BS 30 receives the burst activate acknowledgment message within Tbstact, it transmits a command through a scan message (SCAM_msg.) to an MS, ordering the MS to prepare for the traffic burst (3h). Then, the MS a layer 2 acknowledgment message (Layer 2 Ack. msg.) to the source BS 30 in response to the scan message (3i). The network and the MS exchange forward or reverse traffic burst information for a predetermined time period or until the source BS 30 expands or ends the traffic burst (3j). If timer Tbstact expires, the source BS may choose to resend this message, to terminate traffic burst preparations, or to request that the MSC clear the call association.
The structure of the burst request message transmitted in step 3b is shown in Table 1. The burst request message is an A7 interface message by which a source BS requests reservation of resources to support data traffic burst to a target BS.
TABLE 1Information ElementElement DirectionTypeMessage Type IISource BS > Target BSMCall Connection ReferenceSource BS > Target BSORBand ClassSource BS > Target BSORDownlink Radio EnvironmentSource BS > Target BSORCDMA Serving One Way DelaySource BS > Target BSORPrivacy InfoSource BS > Target BSORA3 Signaling AddressSource BS > Target BSORCorrelation IDSource BS > Target BSORSDU IDSource BS > Target BSORMobile Identity (IMSI/MIN)Source BS > Target BSORMobile Identity (ESN)Source BS > Target BSORFrame Selector InfoSource BS > Target BSORA7 Cell InfoSource BS > Target BSORBurst TimingSource BS > Target BSORM: Mandatory, O: Optional, R: Recommend, C: Conditionally Recommend 
Referring to Table 1, burst request message fields provide information as described below:                1. Call Connection Reference: the only identification used for call connection in the whole system;        2. Band Class: a frequency band;        3. Downlink Radio Environment: a signal strength measurement value provided by a mobile station;        4. CDMA Serving One Way Delay: an estimated value of a single-directional delay in an MS with respect to a cell related with REF_PN;        5. Privacy Info: (public and private) CDMA long code mask information;        6. A3 Signaling Address: network node including an SDU instance in use for a call;        7. Correlation ID: a factor of correlating a request message to a response message;        8. SDU ID: a particular SDU instance ID in one SDU node;        9. Mobile Identity (ESN): Electronic Serial Number (ESN) of an MS;        10. Frame Selector Info: a set of frame selectors used for one call association. This field is used to add a new frame selector to a call association or amend the property of a frame selector in an existing call association;        11. A7 Cell Info: Information about a set of cells to which specific physical cahnnels are added for a call association; and        12. Burst Timing: a factor representative of the period and start time of a data burst on a set of physical channels.        
The structure of the burst response message in step 3c is shown below in Table 2. The burst response message is an A7 interface message as a response for the burst request message (A7-Burst Request msg.) by which the source BS requests reservation of resources to support a data traffic burst to the target BS.
TABLE 2Information ElementElement DirectionTypeMessage Type IISource BS > Target BSMCall Connection ReferenceSource BS > Target BSORCorrelation IDSource BS > Target BSOCA7 Committed Cell InfoSource BS > Target BSORA7 Uncommited Cell InfoSource BS > Target BSORBurst TimingSource BS > Target BSORM: Mandatory, O: Optional, R: Recommend, C: Conditionally Recommend                 1. Call Connection Reference: an identification for a call connection which is unique to the whole system;        2. Correlation ID: a factor of correlating a request message to a response message;        3. A7 Committed Cell Info: information about a set of cells committed to specific physical channels for a call association by a target BS; and        4. A7 Uncommitted Cell Info: information about a set of cells uncommitted to specific physical channels for a call association by a target BS.        
The burst activate message (A7-Burst Activate msg.) in step 3d is shown in Table 3. The burst activate message is an A7 interface message which the source BS transmits to the target BS to commit a set of reserved resources for supporting a data traffic burst.
TABLE 3Information ElementElement DirectionTypeMessage Type IISource BS > Target BSMCall Connection ReferenceSource BS > Target BSORCorrelation IDSource BS > Target BSOCFrame selector InfoSource BS > Target BSORA7 Cell InfoSource BS > Target BSORM: Mandatory, O: Optional, R: Recommend, C: Conditionally Recommend                 1. Call Connection Reference: an identification for a call connection which is unique to the whole system;        2. Correlation ID: a factor of correlating a request message to a response message;        3. Frame Selector Info: a set of frame selectors used for one call association. This field is used to add a new frame selector to a call association or amend the property of a frame selector in an existing call association; and        4. A7 Cell Info: information about a set of cells to which specific physical channels are added for a call association.        
The information elements of the burst activate acknowledgment message (A7-Burst Activate Ack. msg.) in step 3g is shown in Table 4. The burst activate acknowledgment message is an A7 interface response message to the burst activate message which the source BS transmitted to the target BS in order to commit a set of reserved resources for supporting the data traffic burst.
TABLE 4Information elementElement DirectionTypeMessage Type IITarget BS > Source BSMCall Connection ReferenceTarget BS > Source BSORCorrelation IDTarget BS > Source BSOCA7 Uncommited Cell InfoTarget BS > Source BSORM: Mandatory, O: Optional, R: Recommend, C: Conditionally Recommend                 1. Call Connection Reference: an identification for a call connection which is unique to the whole system;        2. Correlation ID: a factor of correlating a request message to a response message; and        3. A7 Uncommitted Cell Info: information about a set of cells uncommitted to specific physical channels for a call association by a target BS.        
Table 5 lists the fields of the Frame Selector Info information element included in the burst request message (A7-Burst Request msg.) shown in Table 1 and the burst activate message (A7-Burst Activate msg.) shown in Table 3.
TABLE 576543210OctetA3/A7 Element Identifier1Length2Count of Frame Selectors3Length of Frame Selector Information4ReservedFrame Selector Index 15Physical Channel Type 16A3 traffic Channel Protocol Stack 17Frame Offset 18Reserved(MSB)9ARFCN1(LSB)10Forward Channel Bandwidth 111Reverse Channel Bandwidth 112ReservedFrame selector Index 213Physical Channel Type 214A3 Traffic Channel Protocol Stack 215Frame Offset 216Reserved(MSB)17ARFCN2(LSB)18Forward Channel Bandwidth 219Reverse Channel Bandwidth 220......ReservedFrame Selector Index amPhysical Channel Type am + 1A3 Traffic Channel Protocol Stack nm + 2Frame Offset nm + 3Reserved(MSB)m + 4ARFCN n(LSB)m + 5Forward Channel Bandwidth nm + 6Reverse Channel Bandwidth nm + 7                1. Count of Frame Selectors: number of frame selectors;        2. Length of Frame Selector Information: the number of octets used to transmit a set of fields for each instance of a frame selector;        3. Frame Selector Index: a binary value used to uniquely indicate a frame selector used for a call association; and        4. Physical Channel Type: the type of a physical channel associated with a designated frame selector. Table 6 below shows the hex values taken by the Physical Channel Type field.        5. Frame Offset: frame offset for a given frame selector;        6. ARFCN (Actual Radio Frequency Channel Number): real radio frequency channel number related with a band class for a call association;        7. Forward Channel Bandwidth: the band of a forward channel assocaited with a frame selector; and        8. Reverse Channel Bandwidth: the band of a reverse channel assocaited with a frame selector.        
TABLE 6Value (Hex)Physical Channel Type01HFundamental Channel (FCH) TIA/EIA/−9502HSupplemental Channel (SCH) TIA/EIA/−9503HDedicated Control Channel (DCCH) TIA/EIA/−958OH to 9FHReserved for UMTSAll other valuesReserved
As shown in Table 6, since the Physical Channel Type field only defines IS-95 channels, and not CDMA-2000 channels, when the CDMA-2000 standard is applied to a mobile communication system, the Base Stations will not be able to identify channels because the CDMA-2000 channels will be confused with IS-95 channels.
The A3 Traffic Channel Protocol Stack is a protocol stack used for an A3 traffic channel attached to a given frame selector. Its structure is shown below, in Table 7.
TABLE 7Value (Hex)Protocol Stack01HAAL2/ATM/Physical LayerAll other valuesReserved
As noted from Table 7, only the AAL2 (ATM Adaptation Layer 2) protocol, which is used for voice service, is defined in the protocol stack used for the A3 traffic channel. Therefore, the protocol stack is not fit for high rate data.
Burst Timing included in the burst request message (A7-Burst Request msg.) shown in Table 1 and the burst response message (A7-Burst Response msg.) shown in Table 2 have the following information elements, shown below in Table 8.
TABLE 876543210OctetA3/A7 Element Identifier1Length2Burst Action Time3(MSB)Burst Duraction4(LSB)5                1. Burst Action Time: accurate start time of a data burst; and        2. Burst Duration: a binary value indicating burst duration expressed in the number of frames. The binary value is the assignment time of an IS-95 SCH and an IS-95B SCCH in IS-2000.        
The above-described conventional technology has the following problems within a BS and between BSs, not with a radio link between a BS and an MS.
There is no way to discriminate between the FCH and SCH in the IS-95B standard and the FCH, DCCH, and SCH in the CDMA-2000 standard with the Frame Selector Info fields shown in Table 5 in the procedure shown in FIG. 3. Therefore, a BS cannot adequately identify channels. Furthermore, high rate data cannot be transmitted since only the AAL2 protocol, which is used for voice service, is defined in the A3 Traffic Channel Protocol Stack.
The duration and start time of a data burst cannot be supported on a concurrent bi-directional SCH or SCCH with the burst timing message of Table 8. The DTX duration of a reverse SCH and SCCH is not provided, thereby making it impossible to perform rapid packet service in a BS. Consequently, a new method should be explored to process high rate data.